1. Field of the Invention
The present invention relates to a process for producing an aqueous dispersion of a polymer substance, and more particularly to a process for producing an aqueous dispersion of a polymer substance, which process enables production of the dispersion in a large amount within a short time, the dispersion having the following characteristics: a narrow distribution of particle size and concentration of the substance; ability to form a protective colloid in a consistent manner; and a variety of applications including imparting water-repellence, anticorrosiveness, and adhesiveness.
2. Background Art
A conventionally known process for producing an aqueous dispersion composition is disclosed in Japanese Patent Application Laid-Open (kokai) No. 304876/1995. In this process, a raw material and a dispersant are placed in a pre-heated kneading apparatus, and the raw material and the dispersant are kneaded by application of shearing force and heated to 160.degree. C. (the softening point of the raw material) or more. Subsequently, after softening and mixing of the raw material is completed, water is added to the resultant mixture, to thereby produce an aqueous dispersion having a predetermined concentration. In this process, asphalt is used as a raw material and partially-saponified poval is used as a dispersant, and poval is allowed to stand six hours or more in advance and is swollen with water to assume the form of sponge block.
However, in the above-described process, raw materials which may be used are limited to substances having a softening point of 160.degree. C. or less. Use of a substance having a softening point of 160.degree. C. or more as a raw material requires a sophisticated kneading apparatus which can effect heating and pressurizing simultaneously, and such an apparatus may contribute to high equipment cost.
Meanwhile, six hours or more are required for swelling partially-saponified poval with water into the form of sponge block, to thereby disadvantageously require a long time for producing a dispersion. In addition, completion of an aqueous dispersion requires about 60 minutes after a raw material is placed into a kneading apparatus, and producing the dispersion in a short time is fundamentally difficult.